A widely used and successful commercial process for synthesizing acetic acid involves the catalyzed carbonylation of methanol with carbon monoxide. The catalyst contains rhodium and/or iridium and a halogen promoter, typically methyl iodide. The reaction is conducted by continuously bubbling carbon monoxide through a liquid reaction medium in which the catalyst is dissolved. The reaction medium also comprises methyl acetate, water, methyl iodide and the catalyst. Conventional commercial processes for carbonylation of methanol include those described in U.S. Pat. Nos. 3,769,329, 5,001,259, 5,026,908, and 5,144,068, the entire contents and disclosures of which are hereby incorporated by reference. Another conventional methanol carbonylation process includes the Cativa™ process, which is discussed in Jones, J. H. (2002), “The Cativa™ Process for the Manufacture of Acetic Acid,” Platinum Metals Review, 44 (3): 94-105 the entire content and disclosure of which is hereby incorporated by reference. The reaction solution is withdrawn from the reactor and purified to obtain acetic acid.
In the commercial production of acetic acid, there are several processes for removing catalysts, promoters and impurities formed during the carbonylation reaction when purifying the acetic acid. In addition to impurities formed during the carbonylation process, some reactants, depending on their source and purity, may contain trace impurities that may pass through the carbonylation process. These “pass-through” impurities may be difficult to remove using conventional purification techniques. Thus, the resulting acetic acid may contain impurities that form an off-specification product that is not suitable for the desired end use.
As a result, the need exists for additional processes for removing impurities, and in particular pass-through impurities, in the production of acetic acid.